Aerial footage on national broadcaster NHK showed fire and smoke billing out of multiple spots in the plant, near Nagoya. An official at the local fire department said fire engines were sent to the site around 12:30 p.m. (0330 GMT).

A spokesman at Nippon Steel said the company was still gathering information.

Shares in Nippon Steel were little changed on the news, down 0.9 percent. (Reporting by Nobuhiro Kubo and Emi Emoto; Writing by Chang-Ran Kim; Editing by Shinichi Saoshiro)